Acupuncture needles stimulate nerves that do not cause the unpleasant feelings of pain that we are trying to treat. They stimulate other nerves that send a more important message to the brain, which is how they block pain. Sometimes animals may react to this sensation as though they are expecting pain, but then relax because it does not occur. Most of the time they accept the fine needles very well and often become relaxed and sleepy during the treatment. Often they appear to look forward to the next treatment when they come back to the practice.